The present invention relates to an Al alloy poppet valve, and especially to an Al alloy poppet valve that provides high strength and high wear resistance.
An intake poppet valve that has relatively low heat load is made of Al alloy to decrease inertia mass in a valve operating system, thereby decreasing engine performance. However, Al alloy valve has low mechanical strength and wear resistance, thereby decreasing durability and reliability.
A poppet valve is made of metal matrix composite (MMC) in which ceramic particles or whiskers are added to heat-treatable Al alloy such as JIS-2000 Alloy (Al-Cu-Mg), JIS-4000 alloy (Al-Si), JIS-6000 alloy (Al-Mg-Si) or JIS-7000 alloy (Al-Zn-Mg-Cu) under Japanese Industrial Standards (JIS). The poppet valve is subjected to melting such as T6 treatment under JIS to increase strength and wear resistance.
In the poppet valve ceramic particles are added to heat-treatable Al alloy and subjected to melting, working temperature of a valve head 250 to 300.degree. C. is higher than solution treatment temperature of 150 to 200.degree. C. when it is used as an intake valve for an engine, so that hardness of the poppet valve increased by solution treatment gradually decreases, and a valve face which requires wear resistance is worn early so that durability is decreased.
To solve the problems, a metal that has wear resistance is padded, or a hardened layer is formed by an alloy which contains reinforcement element. However, the valve head must be heated to temperature above solution treatment temperature, and strength of the whole valve head is decreased.